The invention relates to the treatment of running webs of photographic material, such as exposed and developed photographic films or exposed and developed strips or sheets of photographic paper. More particularly, the invention relates to improvements in methods of and in apparatus for drying moist or wet webs which contain photographic material. As used herein, the term "web" or "webs" is intended to embrace elongated strips as well as discrete sheets of photographic material.
Commonly owned U.S. Pat. No. 4,485,565 granted Dec. 4, 1984 to Franz Ertl et al. discloses an apparatus for drying running strips or sheets of photographic material. In accordance with a feature of the patented invention, the intensity of heat which is radiated by a plurality of heating elements against a running strip or sheet can be varied depending upon the characteristics of the material to be dried. The intensity of radiated heat is selected in advance and remains unchanged in the course of the drying operation. A drawback of such proposal is that the patented apparatus is not ideally suited for the drying of webs of photographic material wherein randomly distributed portions exhibit widely different heat absorptivities due to pronounced differences of opacity. Thus, if a running web includes randomly distributed portions having widely different heat transmissivities, any advance adjustment of the intensity of heat which is directed against and is supposed to reduce the moisture content of a running web is highly unlikely to ensure a desirable uniform drying of the web. The reason is that the less exposed portion of an exposed and developed web is lighter and thus absorbs less heat than a darker portion, i.e., a portion which was exposed to a larger amount of light and is more opaque than the less exposed portion. If a fixed intensity of heat is selected in advance of transport of a web through the drying station, the less exposed portions of the web are likely to be adequately dried and/or the more exposed portions are likely to be damaged as a result of overheating.
The situation is analogous with certain other types of webs (sheets or strips) of photographic material which are to be dried by exposure to radiated heat.